This invention relates to an improved process for manufacturing prefinished hardboard such as fiberboard, particleboard, and other board fabricated from fibers or chips consolidated under pressure and heat to form an integral board material. Flat panel boards of 1/4-, 1/2-, 3/4-inch or larger thicknesses can be produced in varying board sizes such as 4 feet by 8 feet which is typical for use in the construction industry. Other particularly formed objects can be produced by hot pressing fiberous materials in proper matched die presses such as toilet seats and automobile dashboards. Important features in the hardboard manufacturing process include surface sealing of the hardboard product and obtaining a clean release of the pressed hardboard from the hot press mold. U.S. Pat. No. 2,635,976 suggests a binder composition based on phenol-formaldehyde resin and butadiene-styrene latex for binding together the loose fibers and/or chips into an integral composite finished part. More recently issued U.S. Pat. No. 4,009,073 suggests a multi-step process for producing a hardboard as well as disclosing various wet processes and dry processes for manufacturing hardboard, and particularly discloses a process for utilizing so-called "white water". White water is recycled used water previously used in pulp operations and/or used in hardboard processes and often contains considerable impurities such as wood sugars and some lignocellulose fibers. Due to the numerous resinous and lignocellulose materials present in the fibers and chips used in hardboards, sticking to the hot mold is quite a common problem even if a mold release agent is used for coating the mold surface. A further problem in hardboard production is often experienced in the end product wherein the hardboard product surface is subsequently finished in a subsequent process. The hardboard surface must further exhibit excellent holdout to decorative paint coating or patterns so as to avoid uneven or excessive absorption of the paint into the fiberboard surface.
It now has been found that the hardboard process and the hardboard product can be substantially improved by utilizing a pre-press sealer containing a polymer of polyvinyl alcohol in combination with a volatile amine, emulsified fatty acid or esters, and aluminum stearate. The pre-press sealer is applied to the surface of the fiberboard composite prior to inserting the composite hardboard preform into the hot press. The sealer is integrally cured into the fiberboard surface during the hot-pressing step. The resulting sealed fiberboard product produced in accordance with this invention exhibits substantially improved surfaces as well as eliminates sticking of the fiberboard to the press surface. These and other advantages are achieved by the process of this invention.